As seen from the fact that the total volume of shipments of digital still cameras exceeds that of film cameras, the digital still cameras have increasingly been in widespread use. Along this popularization, various levels of users, from high-end users to low-end users, use the digital still cameras and, therefore, the application of the digital still cameras, the required level of the image quality, the preference in the image quality, and so on have become diversified.
For example, users who have used film cameras and are familiar with the image quality of the film cameras tend to prefer “film-camera-like” images when the users compare images captured by digital still cameras with pictures taken by film cameras. In contrast, users who are alienated from images taken by film cameras or still pictures and are familiar to the image quality on TV screens tend to prefer “television-like” image qualities when the users compare images on TV screens with images captured by digital still cameras.
Hence, the manufacturers of the digital still cameras are devising images for every camera type and are developing the image qualities with which assumed target users seem to be satisfied.
As described above, as the user group of digital still cameras becomes large, the preference in the image qualities is diversified. It is considerably difficult in the current state to realize the image qualities satisfying the preferences of the users in one digital still camera. This is because color images captured by digital still cameras are subjected to AWB control (automatic white balance control), tone correction, saturation correction, and so on based on the knowhow unique to each of the manufacturers of the digital still cameras and, then, are recorded in flash memories.
A format compliant with DCF is generally used as an image format when image data is recorded in a flash memory. An sRGB color space, which is a standard color space, is adopted in such a format. In the sRGB color space, tone characteristics or color characteristics including a color gamut (a color reproduction range) of the CRT monitors of personal computers are defined.
In addition, JPEG2000, which is adopted in the DCF and which is an extension of JPEG format, and color spaces that can widely cover the color reproduction range perceived by human beings are considered as image formats. Among these formats or color spaces, an scRGB color space (scene-reference color space) in which the amount of light of a real scene can be stored as linear data, and/or a color space (output-reference color space), for example, an extended sRGB color space, in which the color of data is corrected so as to be appropriate for a destination or a display device, have been internationally standardized.
However, whichever image format is selected, since captured color images are recorded and stored in a flash memory as a simple image in the image format compliant with the DCF, the images satisfying all the image qualities required by various users cannot be stored.
There is another problem in that a captured image becomes a so-called failed image due to an error in setting the basic conditions in the image capture. For example, the color balance of an image can be derogated or the image can be underexposed because of the image capture in a natural light mode below fluorescent light. However, since digital image data is captured in digital still cameras, unlike the images taken by film cameras, there is more need for modification after the image capture.
Countermeasures against the above problems include a method of utilizing commercially available “image correction and processing software” in a personal computer. If a user owns not only a digital still camera but also a personal computer, images captured by the digital still camera can be corrected by using such software to produce appropriate images.
However, the image data which a user can use in the correction is actually data subjected to JPEG compression or the like in the digital still camera. Since the amount of information in the image data is smaller than that of an actual scene, the image cannot necessarily be corrected to the image quality with which the user, particularly, a high-end user, is satisfied.
It is difficult for and troublesome to a low-end user to correct the quality of a captured image to the image quality for which he/she has a preference by the use of the correction and processing software. Accordingly, almost all the commercially available correction and processing software has an “image-quality automatic correction function”, and even a user who has no knowledge of the image correction can simply correct the image. However, under the current conditions, the correction effect can be varied depending on the content of the image and, therefore, a desired image quality cannot often be achieved.
Furthermore, there is a problem of storage in a current sRGB format or a JPEG-YCC format compliant with the current sRGB format in the correction after the image capture. As for the method of storing the image in a scene-reference color space format, such as an scRGB color space or an scYCC color space, a solution is proposed in, for example, Japanese Unexamined Patent Application Publication No. 2001-343753. However, there is currently no image correction software accommodated to the image in the scene-reference color space format.
In order to resolve the problems described above, the present invention provides an image correction method in which a user can correct a captured image to an appropriate or desired image and which can be performed in a digital still camera.